In general, an advantage of amino acid chelates is the fact that they are readily absorbed into absorptive mucosal cells or plant cells by means of active transport or other known mechanisms. In other words, where minerals are absorbed along with amino acids as carrier molecules, it is possible to avoid problems associated with the competition of ions for active sites and the suppression of specific nutritive mineral elements by others.
Amino acid chelates are generally made by reacting alpha-amino acids and metal ions, where the metal ion has a valence of 2 or more, to form a ring structure in a chelate. In such a reaction, the cationic charge of the metal ion is neutralized by the free amino group or carboxyl group of the alpha-amino acid.
These metallic amino acid chelates are represented as the formula below.
wherein M is a divalent metal ion, and R is a side chain of naturally occurring amino acids or peptides. The metal ion includes, for example, calcium, zinc, magnesium, copper, iron, cobalt, manganese, chromium, etc.
Typically, the term “chelate” is defined as a combination of a metal ion and one or more ligands bonded thereto to form a heterocyclic ring structure. In accordance with a definition in the American Association of Feed Control Officials (“AAFCO”), “amino acid chelate” is a product resting from the reaction of a metal ion from a soluble metal salt with amino acids at a molar ratio of two or three moles of amino acid to one mole of metal to form coordinate covalent bonds. In general, the average weight of the hydrolyzed amino acids must be approximately 150 and the resulting molecular weight of the chelate must not exceed 800.
The structure, chemistry and the bioavailability of amino acid chelates are described in a variety of documents, for example, Ashmead et al., Chelated Mineral Nutrition, (1982), Chas. C. Thomas Publishers, Springfield, III.; Ashmead et al., Intestinal Absorption of Metal Ions, (1985); Ashmead et al., Foliar Feeding of Plants with Amino Acid Chelates, (1986); U.S. Pat. No. 4,020,158; U.S. Pat. No. 4,167,564; U.S. Pat. No. 4,216,143; U.S. Pat. No. 4,721,644; U.S. Pat. No. 4,599,152; U.S. Pat. No. 4,774,089; U.S. Pat. No. 4,830,716; U.S. Pat. No. 4,863,898; U.S. Pat. No. 4,725,427 etc.
For reference, it should be understood that the terms “mineral” and “metal ion” as described in this disclosure are used interchangeably.
In the existing methods for preparation of amino acid chelates, where a water soluble salt such as mineral chlorides or sulfates is employed, the reaction condition must be alkaline to more easily perform the reaction. In this case, byproducts tend to be contained in amino acid chelates which may interfere with the synthesis of amino acid chelates or have a negative effect on the absorption thereof in vivo. The reaction formula below as a known method is referred to.
wherein M is a divalent metal ion, and R is a side chain of naturally occurring amino acids or peptides.
Even though the above method provides an electrically neutral amino acid chelate, sulfuric acid dissociates to form anionic sulfate ions and this byproduct interferes with the overall reaction, regardless of whether or not it is present in the form of alkali metal salt and whether or not the sulfate ion takes part in the reaction, and also hinders the adsorption of chelate, per se, in vivo. Moreover, this byproduct is very difficult to separate from the product because the sodium sulfate is water soluble. Furthermore, the reaction of metal sulfate and amino acids does not proceed to 100% completion, thus the sulfuric acid is always present in the reaction system. The same holds true for the presence of chloride ion when utilizing a metal chloride salt, e.g., MCl2, for amino acid chelate preparation.
U.S. Pat. Nos. 6,407,138 and 6,458,981 employ calcium hydroxide and calcium oxide instead of sodium hydroxide, thereby providing an amino acid chelate free of byproducts, but it cannot practically be said that the resulting amino acid chelate is electrically neutral.
The reaction mechanism in U.S. Pat. No. 6,407,138 as mentioned above is represented below.Ca(OH)2+2H(AA)→Ca(AA)2+2H2OCa(AA)2+MSO4→M(AA)2+CaSO4CaO+2H(AA)→Ca(AA)2+H2OCa(AA)2+MSO4→M(AA)2+CaSO4
The reaction mechanism in U.S. Pat. No. 6,458,981 as mentioned above is represented below.Ca(OH)2+H(AA)→Ca(AA)+OH−+H2OCa(AA)+OH−+MSO4→M(AA)+OH−+CaSO4CaO +H(AA)→Ca(AA)+OH−Ca(AA)+OH−MSO4→M(AA)+OH−+H2O
In the above reaction formulas, “AA”s are an amino acid and “M”s are a metal ion.
Referring to these reaction mechanisms, where an amino acid chelate is prepared using calcium hydroxide or calcium oxide, a reaction mixture comprising an electrically neutral amino acid chelate, a cationic amino acid chelate and an anionic hydroxyl group is obtained. Accordingly, it cannot practically be said that the amino acid chelate obtained from these reactions is electrically neutral, as stated previously.